Some research on the photographer Elmer Dyer reveals he was a pioneer in aerial cinematography and is credited on such films as Howard Hughes' Hells Angels. After World War II he started a stock shot business supplying scenes for hundreds of movies and TV shows. This clip appears to be stock shots that may or may not have been used.
Another clue to the date of this clip is the appearance at
2:18 of a young Jim Rathmann. Jim is famous for using his brother's ID to get into races starting in 1946. He was 18 and you needed to be 21 to compete. His birth name was Richard but he had to stick with Jim (his brother's name) because of his continuing successes, later winning the Indy 500 in 1960. He left hot rod racing in California in 1948 for Nascar racing in the midwest. This may not be his first hot rod event but he does look about 18 here so I'm guessing this is most likely from 1946 but possibly 1947.